In recent years, burn-in tests are routinely conducted as a part of a test process for semiconductor related components, and in such a test a voltage is applied to an object for a prolonged period of time (from few hours to tens of hours) at an elevated temperature (approximately 150° C.). It is more and more preferred to conduct such a test on a wafer level (8 inch or 200 mm wafer) rather than on a package level so that the yield factor may be improved. At any event, when applying a contact probe head for simultaneously accessing a large number of points during a burn-in test, the heat resistance and thermal expansion of the support member for electric contact members are important factors that need to be taken into account.
The conductive contact member is desired to be able to accommodate variations in the height of the corresponding electrode on the wafer by resiliently engaging such an electrode. Such an example is illustrated in FIG. 14. Referring to FIG. 14, a plurality of stepped holder holes 2 are passed across the thickness of a support member 21 in the form of a plate member. A small diameter section 2a of each holder hole 2 slidably receives a conductive needle member 23, and a large diameter section 2b of the holder hole 2 receives a conductive coil spring 24. The conductive needle member 23 includes a radial flange 23a which is received in the large diameter section 2b, and is resiliently urged by the coil spring 24 having one end wound around a stem portion 23b extending from the flange 23a. The other end of the coil spring 24 resiliently engages a corresponding terminal 25a of a circuit board 25 which is placed over the support member 21. The terminal 25a is connected to an electric circuit of a tester not shown in the drawing.
A number of such conductive needle members 23 are arranged in parallel to each other in the support member 21 as illustrated in FIG. 14 to form a contact probe head capable of accessing a plurality of points at the same time. An electric test is conducted by pushing such conductive needle members 23 onto the electrodes 26a of a wafer 26 (object to be tested) in a resilient manner.
To allow a plurality of electrodes 26a on the wafer 26 to be accessed at the same time as mentioned above, it is necessary to arrange in the support member 21 a same number of conductive contact members 23 as the number of the electrodes 26a on the wafer 26, and the support member 21 is required to be formed with a large number of holder holes 2 in a precise manner. Furthermore, because an elevated temperature in the order of 120 to 150° C. is maintained for tens of hours in a burn-in test, the contact probe head is required to be provided with a corresponding heat resistance and low thermal coefficient.
The materials having a heat resistance and thermal coefficient comparable to that of silicon serving as the material for a wafer include ceramics, glass and low thermal expansion alloys such as invar as well as silicon. However, machining a silicon member is a time-consuming process, and silicon requires electric insulation. Ceramics are known to be difficult to machine. Glass involves significant dimensional errors when machining, and this results in a poor yield factor. A low thermal expansion alloy is difficult to machine, and requires electric insulation. Therefore, when such materials are selected for the support member of a contact probe head, the production efficiency is low, and the production cost is high.
Plastic material suited for precision machining is suitable as the material for the support member. However, in a contact probe head having a large number of conductive contact members arranged in a support member at a high density, the pressure produced from such a large number of conductive contact members may cause a warping of the support member. The thermal expansion may cause positional errors of the conductive contact members (conductive needle members), and the access point of each conductive contact member may unacceptably offset from the desired point.